Device with a recessed gate electrode that has high thickness uniformity

ABSTRACT

Various embodiments of the present disclosure provide a method for forming a recessed gate electrode that has high thickness uniformity. A gate dielectric layer is deposited lining a recess, and a multilayer film is deposited lining the recess over the gate dielectric layer. The multilayer film comprises a gate electrode layer, a first sacrificial layer over the gate dielectric layer, and a second sacrificial layer over the first sacrificial dielectric layer. A planarization is performed into the second sacrificial layer and stops on the first sacrificial layer. A first etch is performed into the first and second sacrificial layers to remove the first sacrificial layer at sides of the recess. A second etch is performed into the gate electrode layer using the first sacrificial layer as a mask to form the recessed gate electrode. A third etch is performed to remove the first sacrificial layer after the second etch.

REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No.16/822,424, filed on Mar. 18, 2020, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

An integrated circuit (IC) may include low voltage (LV)metal-oxide-semiconductor (MOS) devices and high voltage (HV) MOSdevices. A MOS device comprises a gate electrode and a gate dielectriclayer separating the gate electrode from a substrate. The HV MOS devicesoften have thicker gate dielectric layers than the LV MOS devices andhence often have greater heights than the LV MOS devices. However, thegreater heights may increase the difficulty of integrating amanufacturing process for the HV MOS devices with a manufacturingprocess for the LV MOS devices. Hence, gate electrodes of the HV MOSdevices may be recessed into a substrate to minimize the impact from theincreased height.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of asemiconductor device comprising a recessed gate electrode that has highthickness uniformity.

FIGS. 2A and 2B illustrate top layouts of various embodiments of therecessed gate electrode of FIG. 1 .

FIG. 3 illustrates a cross-sectional view of some embodiments of anintegrated circuit (IC) comprising the semiconductor device of FIG. 1 .

FIG. 4 illustrates a cross-sectional view of some alternativeembodiments of the IC of FIG. 3 in which a trench isolation structureand a channel region are varied.

FIGS. 5A-5F illustrate cross-sectional views of various alternativeembodiments of the IC of FIG. 4 in which the recessed gate electrode isvaried.

FIG. 6 illustrates a cross-sectional view of some alternativeembodiments of the IC of FIG. 3 in which the recessed gate electrode isrecessed into a gate dielectric layer but not a substrate.

FIGS. 7A and 7B illustrate cross-sectional views of various embodimentsof the IC of FIG. 6 in a direction orthogonal to the cross-sectionalview of FIG. 6 .

FIGS. 8A-8C illustrate cross-sectional views of various alternativeembodiments of the IC of FIG. 6 in which the recessed gate electrode isvaried.

FIG. 9 illustrates a cross-sectional view of some alternativeembodiments of the IC of FIG. 6 in which the gate dielectric layeroverlies source/drain regions.

FIG. 10 illustrates a cross-sectional view of some alternativeembodiments of the IC of FIG. 9 in which the recessed gate electrode isvaried.

FIGS. 11-24 illustrate a series of cross-sectional views of someembodiments of a method for forming a semiconductor device comprising arecessed gate electrode that has high thickness uniformity.

FIGS. 25-29 illustrate a series of cross-sectional views of somealternative embodiments of the method of FIGS. 11-24 in which a gateelectrode layer has a recessed surface recessed relative to a topsurface of a gate dielectric layer.

FIGS. 30-34 illustrate a series of cross-sectional views of somealternative embodiments of the method of FIGS. 11-24 in which a gateelectrode layer has a recessed surface elevated above a top surface of agate dielectric layer by a greater amount.

FIG. 35 illustrates a block diagram of some embodiments of the method ofFIGS. 11-34 .

FIGS. 36-43 illustrate a series of cross-sectional views of somealternative embodiments of the method of FIGS. 11-24 in which therecessed gate electrode is formed in place of a dummy structure.

FIGS. 44-49 illustrate a series of cross-sectional views of somealternative embodiments of the method of FIGS. 36-43 in which a gateelectrode layer has a recessed surface recessed relative to a topsurface of a gate dielectric layer.

FIG. 50 illustrates a block diagram of some embodiments of the method ofFIGS. 36-49 .

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Various embodiments of the present disclosure are directed towards amethod for forming a semiconductor device comprising a recessed gateelectrode that has high thickness uniformity, as well as thesemiconductor device resulting from the method. In some embodiments, arecess is formed overlying a substrate. A gate dielectric layer isdeposited lining and partially filling the recess, and a multilayer filmis deposited filling a remainder of the recess over the gate dielectriclayer. The multilayer film comprises a gate electrode layer, a firstsacrificial layer over the gate dielectric layer, and a secondsacrificial layer over the first sacrificial dielectric layer. Aplanarization is performed into the second sacrificial layer and stopson the first sacrificial layer. A first etch is performed into the firstsacrificial layer to remove portions of the first sacrificial layer atsides of the recess. A second etch is performed into the gate electrodelayer using the first sacrificial layer as a mask to remove portions ofthe gate electrode layer at sides of the recess and to form the recessedgate electrode underlying the first sacrificial layer in the recess. Thefirst etch and, in some embodiments, the second etch remove(s) thesecond sacrificial layer. A third etch is performed to remove the firstsacrificial layer. In some embodiments, the first and second etches areperformed by dry etching, whereas the third etch is performed by wetetching. Other etching types are, however, amenable.

In some embodiments, the multilayer film is deposited so each individuallayer of the multilayer film is indented over the recess. As such, aportion of the second sacrificial layer remains directly over the recessupon completion of the planarization. The remaining portion of thesecond sacrificial layer serves as a mask to protect an underlyingportion of the first sacrificial layer during the first etch so thefirst sacrificial layer is not removed from directly over the recess.The first sacrificial layer serves as a mask during the second etch, andpersists to completion of the second etch, so as to protect anunderlying portion of the gate electrode layer that corresponds to therecessed gate electrode. As such, the recessed gate electrode remainsprotected by the first sacrificial layer throughout the second etch andmay have the same thickness that the gate electrode layer was depositedwith.

Because deposition processes may form the gate electrode layer with highthickness uniformity, the recessed gate electrode may have highthickness uniformity. Further, because the recessed gate electroderemains protected by the first sacrificial layer throughout the secondetch, a top surface of the recessed gate electrode may have a highdegree of flatness. The high thickness uniformity and the high degree offlatness may lead to high uniformity with electrical properties of therecessed gate electrode and/or the semiconductor device when thesemiconductor device is manufactured in bulk. For example, a resistanceof the recessed gate electrode and/or a work function of the recessedgate electrode may have high uniformity, such that a threshold voltageof the semiconductor device may have high uniformity.

With reference to FIG. 1 , a cross-sectional view 100 of someembodiments of a semiconductor device 102 comprising a recessed gateelectrode 104 that has high thickness uniformity is provided. Therecessed gate electrode 104 is recessed into a top of a substrate 106.The recessed gate electrode 104 may, for example, be or comprise metal,doped polysilicon, some other suitable conductive material(s), or anycombination of the foregoing. The substrate 106 may, for example be orcomprise a monocrystalline silicon substrate, a silicon-on-insulator(SOI) substrate, or some other suitable semiconductor substrate.

A top surface 104 t of the recessed gate electrode 104 has a high degreeof flatness (e.g., is flat or substantially flat) between a firstfeature 108 a and a second feature 108 b that are respectively onopposite sides of the recessed gate electrode 104 and that are at aperiphery of the recessed gate electrode 104. Further, a thickness T_(g)of the recessed gate electrode 104 has high uniformity (e.g., is uniformor substantially uniform) between the first and second features 108 a,108 b. In at least some embodiments, the top surface 104 t has the highdegree of flatness and the thickness T_(g) has high uniformity becauseof formation of the recessed gate electrode 104 according to a method ofthe present disclosure.

As seen hereafter, at least some embodiments of the method may form therecessed gate electrode 104 from a multilayer film using bothplanarization and etching. Further, the planarization and the etchingmay be performed in a manner that prevents exposure of the recessed gateelectrode 104 to the planarization and that limits exposure of therecessed gate electrode 104 to etchants at a periphery of the recessedgate electrode 104. This limited exposure to the etchants may lead tothe first and second features 108 a, 108 b. Because the recessed gateelectrode 104 is limited to exposure at the periphery of the recessedgate electrode 104, the thickness T_(g) is as deposited at a remainderof the recessed gate electrode 104. Because deposition processes maydeposit material with high thickness uniformity, the thickness T_(g) atthe remainder of the recessed gate electrode 104 may have highuniformity.

In some embodiments, the top surface 104 t of the recessed gateelectrode 104 has a high degree of flatness if a difference between ahighest elevation on the top surface 104 t and a lowest elevation on thetop surface 104 t is less than about 1 percent, 2 percent, 5 percent, orsome other suitable percent of the highest elevation. Further, in someembodiments, the thickness T_(g) has high uniformity if a differencebetween a minimum thickness value and a maximum thickness value is lessthan about 1 percent, 2 percent, 5 percent, or some other suitablepercent of the maximum thickness value. If the top surface 104 t has toomuch variation (e.g., variation greater than about 5 percent or someother suitable percent of the highest elevation), and/or the thicknessT_(g) has too much variation (e.g., variation greater than about 5percent or some other suitable percent of the maximum thickness value),electrical properties of the recessed gate electrode 104 and/orelectrical properties of the semiconductor device 102 may undergo largeshifts and/or may be shifted out of specification. The electricalproperties may include, for example, gate resistance, gate workfunction, threshold voltage, other suitable properties, or anycombination of the foregoing.

In some embodiments, the thickness T_(g) is about 20-200 nanometers,about 20-110 nanometers, about 110-200 nanometers, about 100.16nanometers, about 100.35 nanometers, or some other suitable values. Ifthe thickness T_(g) is too small (e.g., less than about 20 nanometers orsome other suitable value), over etching may extend through the recessedgate electrode 104 during formation of a contact via on the recessedgate electrode 104 and cause damage to a gate dielectric layer 110underlying the recessed gate electrode 104. Such damage may shiftoperating parameters of the semiconductor device 102 out ofspecification and/or degrade performance of the semiconductor device102. If the thickness T_(g) is too large (e.g., greater than about 200nanometers or some other suitable value), integration with othersemiconductor devices on the substrate 106 may be difficult. Forexample, a top surface of the semiconductor device 102 may be elevatedabove top surfaces of the other semiconductor devices to such an extentthat chemical mechanical polish (CMP) loading at semiconductor device102 may be too high. As a result, planarized surfaces may be angledand/or non-uniform instead of substantially horizontal and/orsubstantially flat. This may lead to overlay errors and/or other processdifficulties.

The first and second features 108 a, 108 b are concave recesses and/ordepressions in a top of the recessed gate electrode 104. In alternativeembodiments, the first and second features 108 a, 108 b are upwardprotrusions, inverted rounded corners, or some other suitable features.The first and second features 108 a, 108 b are characterized as featuresbecause the first and second features 108 a, 108 b introducenon-uniformities into the thickness T_(g) of the recessed gate electrode104. As seen hereafter, and briefly mentioned above, the first andsecond features 108 a, 108 b may, for example, be a byproduct of themethod used to form the recessed gate electrode 104.

In some embodiments, the first feature 108 a is a mirror image of thesecond feature 108 b. Further, in some embodiments, the first and secondfeatures 108 a, 108 b occupy a small percentage of surface area in atwo-dimensional (2D) projection of the recessed gate electrode 104 ontoa top surface of the substrate 106 and/or onto a horizontal plane. The2D projection of the recessed gate electrode 104 may, for example, alsobe known as a footprint of the recessed gate electrode 104. The smallpercentage may, for example, be a percentage less than about 5, 10, or20 percent or some other suitable percentage.

Because the first and second features 108 a, 108 b introducenon-uniformities into the thickness T_(g) of the recessed gate electrode104, the thickness T_(g) becomes more uniform as the first and secondfeatures 108 a, 108 b occupy less surface area. If the first and secondfeatures 108 a, 108 b occupy too much surface area (e.g., greater thanabout 20 percent or some other suitable percentage), electricalproperties of the recessed gate electrode 104 may undergo large shiftsand/or may be shifted out of specification.

The gate dielectric layer 110 cups an underside of the recessed gateelectrode 104 and separates the recessed gate electrode 104 from thesubstrate 106. The gate dielectric layer 110 may be or comprise, forexample, silicon oxide and/or some other suitable dielectric(s).Further, a pair of source/drain regions 112 is in the substrate 106. Thesource/drain regions 112 are respectively on opposite sides of therecessed gate electrode 104. The source/drain region 112 may be orcomprise, for example, a doped semiconductor region of the substrate 106and/or an epitaxial layer grown on the substrate 106.

A channel region 106 c underlies the recessed gate electrode 104 in thesubstrate 106 and extends from one of the source/drain regions 112 toanother one of the source/drain regions 112. The channel region 106 c isconfigured to change between a conductive state and a non-conductivestate depending upon a bias voltage applied to the recessed gateelectrode 104. For example, the channel region 106 c may change to theconducting state when the recessed gate electrode 104 is biased with avoltage above a threshold voltage. As another example, the channelregion 106 c may change to the non-conducting state when the recessedgate electrode 104 is biased with a voltage below the threshold voltage.

In some embodiments, the semiconductor device 102 is a field-effecttransistor (FET), some other suitable transistor, a memory cell, or someother suitable semiconductor device. In some embodiments, thesemiconductor device 102 is large. The semiconductor device 102 may, forexample, be large when a width W_(g) of the recessed gate electrode 104is greater than about 20 micrometer, 30 micrometers, or some othersuitable value. Further, the semiconductor device 102 may, for example,have such a large width when used for a HV application or some othersuitable application. A high voltage (HV) application may, for example,be an application in which he semiconductor device 102 operates atvoltages in excess of 100 volts, 200 volts, 600 volts, 1200 volts, orsome other suitable value.

With reference to FIGS. 2A and 2B, top layouts 200A, 200B of variousembodiments of the recessed gate electrode 104 of FIG. 1 is provided.The cross-sectional view 100 of FIG. 1 may, for example, be taken alongline A in either one of FIGS. 2A and 2B or along some other suitableline (not shown) in either one of FIGS. 2A and 2B.

The first and second features 108 a, 108 b correspond to regions of aring-shaped feature 108 (shown in phantom) extending in a closed pathalong an edge of the recessed gate electrode 104. In FIG. 2A, therecessed gate electrode 104 is square shaped and the ring-shaped feature108 is square ring shaped. In FIG. 2B, the recessed gate electrode 104is circular and the ring-shaped feature 108 is circular ring shaped.While FIGS. 2A and 2B provide specific shapes for the recessed gateelectrode 104 and the ring-shaped feature 108, other shapes are amenablefor the recessed gate electrode 104 and the ring-shaped feature 108.

With reference to FIG. 3 , a cross-sectional view 300 of someembodiments of an integrated circuit (IC) comprising the semiconductordevice 102 of FIG. 1 is provided. The semiconductor device 102 issurrounded by a trench isolation structure 302. The trench isolationstructure 302 extends into a top of the substrate 106 and provideselectrical isolation between the semiconductor device 102 and othersemiconductor devices (not shown). The trench isolation structure 302 isor comprises silicon oxide and/or some other suitable dielectric(s).Further, the trench isolation structure 302 may be or comprise, forexample, a shallow trench isolation (STI) structure or some othersuitable trench isolation structure.

An interconnect structure 304 overlies the substrate 106 and thesemiconductor device 102 and comprises an interlayer dielectric (ILD)layer 306 and a plurality of contact vias 308. The contact vias 308 arein the ILD layer 306 and extend respectively to the source/drain regions112 and the recessed gate electrode 104. In some embodiments, theinterconnect structure 304 further comprise a plurality of wires (notshown) and a plurality of inter-wire vias (not shown) alternatinglystacked over the contact vias 308 to define conductive paths leadingfrom the contact vias 308. The ILD layer 306 may be or comprise, forexample, silicon oxide and/or some other suitable dielectric(s). Thecontact vias 308 may be or comprise, for example, metal and/or someother suitable conductive material(s).

A silicide layer 310 is on the recessed gate electrode 104 and providesohmic coupling between the recessed gate electrode 104 and acorresponding contact via. In alternative embodiments, the silicidelayer 310 is omitted. Further, in alternative embodiments, silicidelayers (not shown) are on the source/drain regions 112 to provide ohmiccoupling between the source/drain regions 112 and corresponding contactvias. The silicide layer 310 may be or comprise, for example, nickelsilicide and/or some other suitable metal silicide.

A hard mask 312 is on the recessed gate electrode 104 and the gatedielectric layer 110. The hard mask 312 has a pair of segmentsrespectively bordering opposite edges of the silicide layer 310, and thesegments extend respectively from the source/drain regions 112respectively to the opposite edges. As seen hereafter, the hard mask 312may, for example, be employed as a mask during formation of thesource/drain regions 112 and/or the silicide layer 310. The hard mask312 may, for example, be or comprise silicon nitride, silicon oxide,some other suitable dielectric(s), or any combination of the foregoing.

A base dielectric layer 314 is on the trench isolation structure 302 andthe substrate 106 at sides of the gate dielectric layer 110 and isbetween the hard mask 312 and the substrate 106. Further, a contact etchstop layer (CESL) 316 is on the base dielectric layer 314 and the hardmask 312. As seen hereafter, the CESL 316 may be used as an etch stopwhile etching openings within which contact vias corresponding to thesource/drain regions 112 are formed. The base dielectric layer 314 maybe or comprise, for example, silicon oxide and/or some other suitabledielectric(s). The CESL 316 may, for example, be or comprise siliconnitride and/or some other suitable dielectric(s).

With reference to FIG. 4 , a cross-sectional view 400 of somealternative embodiments of the IC of FIG. 3 is provided in which asegment 302 a of the trench isolation structure 302 separates aneighboring source/drain region 112 a from the recessed gate electrode104. As a result, the channel region 106 c conforms around a bottom ofthis trench isolation segment 302 a and has an increased length.Further, a portion of the channel region 106 c at the neighboringsource/drain region 112 a and the trench isolation segment 302 a isfarther from the recessed gate electrode 104 than a remainder of thechannel region 106 c. As a result, this portion of the channel region106 c depends upon a stronger electric field to change betweenconducting and non-conducting states than the remainder of the channelregion 106 c. This, in turn, allows the semiconductor device 102 tooperate at higher voltages.

With reference to FIGS. 5A-5F, cross-sectional views 500A-500F ofvarious alternative embodiments of the IC of FIG. 4 are provided inwhich the recessed gate electrode 104 is varied. In FIG. 5A, the firstand second features 108 a, 108 b are inverted rounded and/or depressedcorners. In some embodiments, the inverted rounded and/or depressedcorners arc downward with a decreasing slope continuously from a topsurface of the recessed gate electrode 104 to a sidewall of the recessedgate electrode 104. In FIG. 5B, the first and second features 108 a, 108b are protrusions that protrude upward and that have rounded tops. InFIG. 5C, the first and second features 108 a, 108 b are protrusions thatprotrude upward and that have flat or substantially flat tops. In FIG.5D, the first and second features 108 a, 108 b are protrusions thatprotrude upward and that have top surfaces with concave recesses.

In both FIGS. 5E and 5F, the recessed gate electrode 104 and the gatedielectric layer 110 are less rectilinear and have, among other things,more rounded edges and more slanted sidewalls. In FIG. 5E, the first andsecond features 108 a, 108 b are protrusions. In FIG. 5F, the recessedgate electrode 104 partially overlies a segment 302 a of the trenchisolation structure 302 and has a bottom surface that is uneven andchanges elevation at the segment 302 a. Further, the thickness T_(g) ofthe recessed gate electrode 104 increases towards a source/drain region112 a neighboring the segment 302 a of the trench isolation structure302. Arranging the recessed gate electrode 104 over the trench isolationsegment 302 a may enable the semiconductor device 102 to operate athigher voltage because the trench isolation structure 302 dissipates anelectric field produced by the recessed gate electrode 104.

While FIGS. 2A and 2B are described with regard to the recessed gateelectrode 104 of FIG. 1 , it is to be appreciated that FIGS. 2A and 2Bare applicable to the recessed gate electrode 104 in any one of FIGS. 3,4, and 5A-5F. For example, any one of FIGS. 3, 4, and 5A-5F may be takenalong line A in either one of FIGS. 2A and 2B or along some othersuitable line (not shown) in either one of FIGS. 2A and 2B. While thetrench isolation structure 302 and the channel region 106 c in FIGS.5A-5F are configured as in FIG. 4 , the trench isolation structure 302and the channel region 106 c may alternatively be configured as in FIGS.1 and 3 .

With reference to FIG. 6 , a cross-sectional view 600 of somealternative embodiments of the IC of FIG. 3 is provided in which therecessed gate electrode 104 is recessed into the gate dielectric layer110 but not the substrate 106. Further, the source/drain regions 112have top surfaces elevated above a top surface of the substrate 106, thebase dielectric layer 314 and the hard mask 312 are omitted, and theCESL 316 is on sidewalls of the gate dielectric layer 110. Inalternative embodiments, the base dielectric layer 314 and/or the hardmask 312 remain(s).

With reference to FIGS. 7A and 7B, cross-sectional views 700A, 700B ofvarious embodiments of the IC of FIG. 6 in a direction orthogonal to thecross-sectional view 600 of FIG. 6 is provided. The cross-sectionalviews 700A, 700B of FIGS. 7A and 7B are alternative embodiments of eachother, and the cross-sectional view 600 of FIG. 6 may, for example, betaken along line B in either one of FIGS. 7A and 7B. In FIG. 7A, thesemiconductor device 102 is a planar FET, such that a bottom surface ofthe recessed gate electrode 104 is planar or substantially planar. InFIG. 7B, the semiconductor device 102 is a finFET, such that the bottomsurface of the recessed gate electrode 104 wraps around a top of findefined by the substrate 106. In both FIGS. 7A and 7B, the semiconductordevice 102 partially overlies the trench isolation structure 302.

With reference to FIGS. 8A-8C, cross-sectional views 800A-800C ofvarious alternative embodiments of the IC of FIG. 6 are provided inwhich the recessed gate electrode 104 is varied. In FIG. 8A, the firstand second features 108 a, 108 b are inverted rounded corners. In FIG.8B, the first and second features 108 a, 108 b are protrusions thatprotrude upward and that have rounded tops. In FIG. 8C, the first andsecond features 108 a, 108 b are protrusions that protrude upward andthat have flat or substantially flat tops. In alternative embodiments,the recessed gate electrode 104 may be as in any one of FIGS. 1, 3, 4,and 5A-5F.

With reference to FIG. 9 , a cross-sectional view 900 of somealternative embodiments of the IC of FIG. 6 is provided in which thegate dielectric layer 110 overlies the source/drain regions 112.Further, the first and second features 108 a, 108 b are more symmetricaland a top surface of the recessed gate electrode 104 is elevated above atop surface of the gate dielectric layer 110. In alternativeembodiments, the top surface of the recessed gate electrode 104 may beabout even with or recessed below the top surface of the gate dielectriclayer 110.

With reference to FIG. 10 , a cross-sectional view 1000 of somealternative embodiments of the IC of FIG. 9 is provided in which thefirst and second features 108 a, 108 b are protrusions that protrudeupward and that have top surfaces that are flat or substantially flat.Further, the top surfaces of the protrusions are about even with a topsurface of the gate dielectric layer 110. In alternative embodiments,the top surfaces of the protrusions may be elevated above or recessedbelow the top surface of the gate dielectric layer 110. In alternativeembodiments, the recessed gate electrode 104 may be as in any one ofFIGS. 1, 3, 4, 5A-5F, 6, 7A, 7B, and 8A-8C.

While FIGS. 2A and 2B are described with regard to the recessed gateelectrode 104 of FIG. 1 , it is to be appreciated that FIGS. 2A and 2Bare applicable to the recessed gate electrode 104 in any one of FIGS. 6,7A, 7B, 8A-8C, 9, and 10 . For example, any one of FIGS. 6, 7A, 7B,8A-8C, 9, and 10 may be taken along line A in either one of FIGS. 2A and2B or along some other suitable line (not shown) in either one of FIGS.2A and 2B. While FIGS. 7A and 7B are described with regard to thesemiconductor device 102 of FIG. 6 , it is to be appreciated that FIGS.7A and 7B are applicable to the semiconductor device 102 in any one ofFIGS. 8A-8C, 9, and 10 . For example, any one of FIGS. 8A-8C, 9, and 10may be taken along line B in either one of FIGS. 7A and 7B or along someother suitable line (not shown) in either one of FIGS. 7A and 7B.

With reference to FIGS. 11-24 , a series of cross-sectional views1100-2400 of some embodiments of a method for forming a semiconductordevice comprising a recessed gate electrode that has high thicknessuniformity is provided. The cross-sectional views 1100-2400 correspondto the cross-sectional view 400 of FIG. 4 and therefore illustrateformation of the IC and the semiconductor device 102 in FIG. 4 .However, the method illustrated by the cross-sectional views 1100-2400may also be employed to form the IC and/or the semiconductor device 102in any of FIGS. 1, 3, 4, and 5A-5F.

As illustrated by the cross-sectional view 1100 of FIG. 11 , a substrate106 is provided. The substrate 106 is covered by a first base dielectriclayer 314 and a second base dielectric layer 1102. Further, a trenchisolation structure 302 extends into a top of the substrate 106 and isalso covered by the first and second base dielectric layers 314, 1102.The second base dielectric layer 1102 may be or comprise, for example,silicon nitride and/or some other suitable dielectric(s). In someembodiments, the first base dielectric layer 314 is or comprise siliconoxide, whereas the second base dielectric layer 1102 is or comprisesilicon nitride.

Also illustrated by the cross-sectional view 1100 of FIG. 11 , thesubstrate 106 is patterned to form a recess 1104 extending into thesubstrate 106 to a depth D₁. The depth D₁ may, for example, be about500-1500 angstroms, about 500-1000 angstroms, about 1000-1500 angstroms,about 1000 angstroms, or some other suitable value. The patterning may,for example, be performed by a photolithography/etching process or someother suitable process. The photolithography/etching process may, forexample, employ a photoresist mask 1106 and/or some other suitable maskoverlying the second base dielectric layer 1102.

As illustrated by the cross-sectional view 1200 of FIG. 12 , a gatedielectric layer 110 is deposited overlying the second base dielectriclayer 1102 and lining the recess 1104. The gate dielectric layer 110 isrecessed at the recess 1104 and may be or comprise, for example, siliconoxide and/or some other suitable dielectric(s).

Also illustrated by the cross-sectional view 1200 of FIG. 12 , amultilayer film 1202 is deposited over the gate dielectric layer 110 andlining the recess 1104. The multilayer film 1202 comprises a gateelectrode layer 1204, a first sacrificial layer 1206, and a secondsacrificial layer 1208 each individually recessed at the recess 1104.The gate electrode layer 1204 is conductive and may be or comprise, forexample, doped polysilicon, metal, some other suitable conductivematerial(s), or any combination of the foregoing. The first sacrificiallayer 1206 overlies the gate electrode layer 1204 and may be orcomprise, for example, silicon nitride, silicon oxide, siliconoxynitride, some other suitable dielectric(s), or any combination of theforegoing. The second sacrificial layer 1208 overlies the firstsacrificial layer 1206 and is a different material than the firstsacrificial layer 1206. The second sacrificial layer 1208 may be siliconoxide and/or some other suitable dielectric(s). Alternatively, thesecond sacrificial layer 1208 may be metal, doped polysilicon, someother suitable conductive material(s), or any combination of theforegoing. In some embodiments, the gate electrode layer 1204 and thesecond sacrificial layer 1208 are or comprise the same material.Further, in some embodiments, the gate electrode layer 1204 is orcomprise doped polysilicon, the first sacrificial layer 1206 is orcomprise silicon nitride, and the second sacrificial layer 1208 is orcomprise silicon oxide.

In some embodiments, the gate dielectric layer 110 and the individuallayers of the multilayer film 1202 are conformally deposited. Further,in some embodiments, the gate dielectric layer 110 and the individuallayers of the multilayer film 1202 are deposited by chemical vapordeposition (CVD), physical vapor deposition (PVD), some other suitabledeposition process(es), or any combination of the foregoing.

The gate electrode layer 1204 is deposited with a thickness T_(g) thatcorresponds to a final thickness for a recessed gate electrode hereafterformed from the gate electrode layer 1204. Because CVD, PVD, and othersuitable deposition processes may form the gate electrode layer 1204with high thickness uniformity, the recessed gate electrode may havehigh thickness uniformity. The high thickness uniformity may lead tohigh uniformity with electrical properties of the recessed gateelectrode and/or the semiconductor device when the semiconductor deviceis manufactured in bulk. For example, a resistance of the recessed gateelectrode and/or a work function of the recessed gate electrode may havehigh uniformity, such that a threshold voltage of the semiconductordevice may have high uniformity.

Further, the thickness T_(g) is such that a recessed surface 1204 r ofthe gate electrode layer 1204 is elevated above a top surface of thegate dielectric layer 110 by a distance D₂. In alternative embodiments,embodiments, the thickness T_(g) is such that the recessed surface 1204r of the gate electrode layer 1204 is about even with the top surface ofthe gate dielectric layer 110 (e.g., the distance D₂ is about zero). Aswill be seen hereafter, variations in the thickness T_(g) may lead tothe recessed gate electrode having different profiles.

As illustrated by the cross-sectional view 1300 of FIG. 13 , a firstplanarization is performed into the second sacrificial layer 1208 andstops on the first sacrificial layer 1206. The first planarization may,for example, be performed by a CMP and/or some other suitableplanarization process. Because the first planarization stops on thefirst sacrificial layer 1206 and the first sacrificial layer 1206 isrecessed at the recess 1104, the second sacrificial layer 1208 remainsat the recess 1104. Further, in at least embodiments in which the firstplanarization is performed by a CMP, different CMP removal rates maylead to dishing at the second sacrificial layer 1208. As such, the topsurface 1208 t of the second sacrificial layer 1208 may be concaveand/or a thickness T_(s) of the second sacrificial layer 1208 may benon-uniform.

As illustrated by the cross-sectional view 1400 of FIG. 14 , a firstetch is performed into the multilayer film 1202. The first etch removesportions of the first sacrificial layer 1206 at sides of the recess 1104and uncovered by the second sacrificial layer 1208 (see, e.g., FIG. 13). As a result, the first sacrificial layer 1206 has a pair ofprotrusions 1402 at a periphery of the first sacrificial layer 1206 andrespectively on opposite sides of the first sacrificial layer 1206.Additionally, the first etch thins the gate electrode layer 1204 andremoves the second sacrificial layer 1208 (see, e.g., FIG. 13 ). Inalternative embodiments, the first etch doesn't remove the secondsacrificial layer 1208 but instead thins the second sacrificial layer1208. Regardless of whether the second sacrificial layer 1208 is removedor merely thinned by the first etch, the second sacrificial layer 1208serves as a mask to protect underlying portions of the first sacrificiallayer 1206. But for the second sacrificial layer 1208, the portion ofthe first sacrificial layer 1206 overlying the recess 1104 would beremoved or substantially thinned.

In some embodiments, the first etch is performed with a non-selectiveetchant. The non-selective etchant may, for example, be non-selective inthat it has the same or substantially the same etch rates for the firstsacrificial layers 1206 as for the second sacrificial layer 1208 and/orthe gate electrode layer 1204. In alternative embodiments, the firstetch is performed with a selective etchant that has high selectivity(e.g., a high etch rate) for the first sacrificial layer 1206 relativeto the second sacrificial layer 1208 and/or the gate electrode layer1204. In some embodiments, the first etch is performed by dry etching.In alternative embodiments, the first etch is performed by wet etchingand/or some other suitable type of etching.

As illustrated by the cross-sectional view 1500 of FIG. 15 , a secondetch is performed into the gate electrode layer 1204 and stops on thefirst sacrificial layer 1206 and the gate dielectric layer 110. Thesecond etch removes portions of the gate electrode layer 1204 at sidesof the recess 1104 and uncovered by the first sacrificial layer 1206. Asa result, the second etch forms a recessed gate electrode 104 in therecess 1104. Further, the second etch removes any remaining portion ofthe second sacrificial layer 1208 (see, e.g., FIG. 13 ).

The first sacrificial layer 1206 serves as a mask to protect underlyingportions of the gate electrode layer 1204. Because the first sacrificiallayer 1206 protects the gate electrode layer 1204 and the second etchstops on the first sacrificial layer 1206, the thickness T_(g) of therecessed gate electrode 104 is the same thickness that the gateelectrode layer 1204 (see, e.g., FIG. 12 ) was deposited as where therecessed gate electrode 104 is covered by the first sacrificial layer1206. Because the gate electrode layer 1204 may be deposited with highthickness uniformity, the recessed gate electrode 104 may have highthickness uniformity. The high thickness uniformity may lead to highuniformity with electrical properties of the recessed gate electrode 104when the recessed gate electrode 104 is manufactured in bulk.

Because the recessed gate electrode 104 is uncovered by the firstsacrificial layer 1206 at a periphery of the recessed gate electrode104, the second etch over etches into the recessed gate electrode 104 atthe periphery of the recessed gate electrode 104. As a result, a firstfeature 108 a and a second feature 108 b may be formed at the peripheryof the recessed gate electrode 104, respectively on opposite sides ofthe recessed gate electrode 104. A top layout of the recessed gateelectrode 104 may, for example, be as in either one of FIGS. 2A and 2Band/or the cross-sectional view 1500 of FIG. 15 may, for example, betaken along line A in either one of FIGS. 2A and 2B. Other top layoutsare, however, amenable.

The second etch is performed with a selective etchant that has a highetch rate for the gate electrode layer 1204 relative to the firstsacrificial layer 1206 and/or the gate dielectric layer 110. In someembodiments, the second etch is performed by dry etching. In alternativeembodiments, the second etch is performed by wet etching and/or someother suitable type of etching. However, dry etching may achieve higherselectivity than wet etching. Because of the higher selectivity, dryetching is less likely to etch through the first sacrificial layer 1206at the recessed gate electrode 104 than wet etching. Hence, dry etchingis less likely than wet etching to cause damage to the recessed gateelectrode 104.

In some embodiments, the first and second etches are performed within acommon process chamber, such that the substrate 106 remains in thecommon process chamber from a beginning of the first etch to an end ofthe second etch. In alternative embodiments, the first and second etchesare performed in separate process chamber. In some embodiments, thefirst and second etches are performed by the same etch type. Forexample, the first and second etches may be performed by dry etching. Inalternative embodiments, the first and second etches are performed bydifferent etch types. For example, the first etch may be performed bywet etching, whereas the second etch may be performed by dry etching, orvice versa.

In some embodiments, the first and second etches are performed by dryetching within a common process chamber and define a common dry etchprocess. The common dry etch process may, for example, compriseperforming the first etch with a first set of process gases in thecommon process chamber, transitioning from the first set of processgases to a second set of process gases in the common process chamber,and performing the second etch with the second set of process gases inthe common process chamber.

As illustrated by the cross-sectional view 1600 of FIG. 16 , a thirdetch is performed into the first sacrificial layer 1206 (see, e.g., FIG.15 ). The third etch removes the first sacrificial layer 1206. Further,in some embodiments, the third etch rounds corners of the recessed gateelectrode 104 and/or rounds corners of the gate dielectric layer 110.The third etch is performed using an etchant having a high selectivity(e.g., a high etch rate) for the first sacrificial layer 1206 relativeto the recessed gate electrode 104 so the recessed gate electrode 104 isnot etched and/or is minimally etched.

In some embodiments, the third etch is performed by wet etching. Forexample, the third etch may be performed by wet etching using an etchantcomprising phosphoric acid (e.g., H₃PO₄) in at least some embodiments inwhich the first sacrificial layer 1206 is or comprises silicon nitride.As another example, the third etch may be performed by wet etching usingan etchant comprising dilute hydrofluoric acid (DHF) in at least someembodiments in which the first sacrificial layer 1206 is or comprisessilicon oxide. Other suitable etchants are, however, amenable for thethird etch. In alternative embodiments, the second etch process isperformed by dry etching and/or some other suitable etching type.However, physical ion bombardment by dry etching is more likely to causedamage to the recessed gate electrode 104 than wet etching. Hence, dryetching is more likely to lead to non-uniformity in the thickness T_(g)of the recessed gate electrode 104. As noted above, such non-uniformityin the thickness T_(g) may lead to non-uniformity with electricalproperties of the recessed gate electrode 104 when the recessed gateelectrode 104 is manufactured in bulk.

As illustrated by the cross-sectional view 1700 of FIG. 17 , a fourthetch is performed into the gate dielectric layer 110. The fourth etchremoves portions of the gate dielectric layer 110 overlying the secondbase dielectric layer 1102. Further, the fourth etch rounds corners 1702of the recessed gate electrode 104 at the first and second features 108a, 108 b. The fourth etch is performed using an etchant having a highselectivity (e.g., a high etch rate) for the gate dielectric layer 110relative to the recessed gate electrode 104 so the recessed gateelectrode 104 is not etched and/or is minimally etched.

In some embodiments, the fourth etch is performed by wet etching. Forexample, the fourth etch may be performed by wet etching using anetchant comprising DHF in at least some embodiments in which the gatedielectric layer 110 is or comprises silicon oxide. Other suitableetchants are, however, amenable for the fourth etch. In alternativeembodiments, the fourth etch is performed by dry etching and/or someother suitable etching type. However, ion bombardment by dry etching ismore likely than wet etching to cause damage to the recessed gateelectrode 104.

In some embodiments, the gate dielectric layer 110 and the firstsacrificial layer 1206 (see, e.g., FIG. 15 ) are or comprise the samematerial. For example, the gate dielectric layer 110 and the firstsacrificial layer 1206 may be or comprise silicon oxide. In at leastsome embodiments in which the gate dielectric layer 110 and the firstsacrificial layer 1206 are or comprise the same material, the third andfourth etches are performed together by the same act of etching. Forexample, the third and fourth etches may be performed together by wetetching using DHF in at least some embodiments in which the gatedielectric layer 110 and the first sacrificial layer 1206 are orcomprise silicon oxide. Accordingly, the gate dielectric layer 110 andthe first sacrificial layer 1206 are removed simultaneously in someembodiments.

As illustrated by the cross-sectional view 1800 of FIG. 18 , a fifthetch is performed into the second base dielectric layer 1102. The fifthetch removes the second base dielectric layer 1102. Further, the fifthetch further rounds the corners 1702 of the recessed gate electrode 104at the first and second features 108 a, 108 b. The fifth etch isperformed using an etchant having a high selectivity (e.g., a high etchrate) for the second base dielectric layer 1102 relative to the recessedgate electrode 104 so the recessed gate electrode 104 is not etchedand/or is minimally etched.

In some embodiments, the fifth etch is performed by wet etching. Forexample, the fifth etch may be performed by wet etching using an etchantcomprising phosphoric acid (e.g., H₃PO₄) in at least some embodiments inwhich the second base dielectric layer 1102 is or comprises siliconnitride. Other suitable etchants are, however, amenable for the fifthetch. In alternative embodiments, the fifth etch is performed by dryetching and/or some other suitable etching type. However, ionbombardment by dry etching is more likely than wet etching to causedamage to the recessed gate electrode 104.

In some embodiments, the first and second etches are performed by dryetching and/or define a multi-step dry etch process, whereas the third,fourth, and fifth etches are performed by wet etching and/or define amulti-step wet etch process. In some embodiments, the second basedielectric layer 1102 (see, e.g., FIG. 17 ) and the first sacrificiallayer 1206 (see, e.g., FIG. 15 ) are or comprise silicon nitride,whereas the gate dielectric layer 110 is or comprises silicon oxide. Inat least some of such embodiments, the third and fifth etches areperformed by wet etching using etchants comprising phosphoric acid,whereas the fourth etch is performed by wet etching using an etchantcomprising DHF.

As illustrated by the cross-sectional view 1900 of FIG. 19 , a hard masklayer 1902 is deposited over recessed gate electrode 104 and thesubstrate 106. The hard mask layer 1902 may be or comprise, for example,silicon nitride, silicon oxide, some other suitable dielectric(s), orany combination of the foregoing.

As illustrated by the cross-sectional view 2000 of FIG. 20 , the hardmask layer 1902 (see, e.g., FIG. 19 ) is patterned to remove the hardmask layer 1902 from sides of the recessed gate electrode 104 and toform a hard mask 312 overlying the recessed gate electrode 104. Thepatterning may, for example, be performed by a photolithography/etchingor some other suitable patterning process. The photolithography/etchingprocess may, for example, employ a photoresist mask 2002 and/or someother suitable mask overlying the hard mask layer 1902.

As illustrated by the cross-sectional view 2100 of FIG. 21 , a pair ofsource/drain regions 112 are formed in the substrate 106. Thesource/drain regions 112 are formed respectively on opposite sides ofthe recessed gate electrode 104. The source/drain regions 112 may, forexample, be formed by ion implantation into the substrate 106, anepitaxial deposition process, some other suitable process, or anycombination of the foregoing. The recessed gate electrode 104, the gatedielectric layer 110, and the source/drain regions 112 partially orwholly define a semiconductor device 102. The semiconductor device 102may be, for example, a FET, some other suitable transistor, a memorycell, or some other suitable semiconductor device.

Also illustrated by the cross-sectional view 2100 of FIG. 21 , a CESL316 and a first ILD layer 306 a are deposited over the hard mask 312 andthe substrate 106. The first ILD Layer 306 a may, for example, be orcomprise silicon oxide and/or some other suitable dielectric(s).

As illustrated by the cross-sectional view 2200 of FIG. 22 , a secondplanarization is performed into the first ILD layer 306 a and the CESL316 to expose the hard mask 312. Further, the second planarizationcoplanarize a top surface of the first ILD layer 306 a and a top surfaceof the CESL 316 with a top surface of the hard mask 312. The secondplanarization may, for example, be performed by a CMP and/or some othersuitable planarization process.

As illustrated by the cross-sectional view 2300 of FIG. 23 , the hardmask 312 is patterned to form an opening 2302 exposing the recessed gateelectrode 104. The patterning may, for example, be performed by aphotolithography/etching or some other suitable patterning process. Thephotolithography/etching process may, for example, employ a photoresistmask 2304 and/or some other suitable mask overlying the hard mask 312.

Also illustrated by the cross-sectional view 2300 of FIG. 23 , asilicide layer 310 is formed on the recessed gate electrode 104, in theopening 2302. The silicide layer 310 may, for example, be formed by asalicide process and/or some other suitable silicide formation process.

As illustrated by the cross-sectional view 2400 of FIG. 24 , a secondILD layer 306 b is formed filling the opening 2302 (see, e.g., FIG. 23 )and further overlying the first ILD layer 306 a and the silicide layer310. The second ILD layer 306 b may, for example, be or comprise siliconoxide and/or some other suitable dielectric(s). A process for formingthe second ILD layer 306 b may, for example, comprise depositing thesecond ILD layer 306 b and subsequently performing a planarization intoa top surface of the second ILD layer 306 b.

Also illustrated by the cross-sectional view 2400 of FIG. 24 , contactvias 308 are formed in the second ILD layer 306 b, extendingrespectively from the source/drain regions 112 and the silicide layer310. A process for forming the contact vias 308 may, for example,comprise selectively etching the first and second ILD layers 306 a, 306b to form contact openings, depositing conductive material in thecontact openings, and planarizing the conductive material. Otherprocesses are, however, amenable.

Because the recessed gate electrode 104 is formed according to themethod of the present disclosure, the thickness T_(g) of the recessedgate electrode 104 has high uniformity and the recessed gate electrode104 is less likely to be too thin at a center of the recessed gateelectrode 104. If the recessed gate electrode 104 were to get too thinat the center of the recessed gate electrode 104, formation of thecontact vias 308 may over etch through the recessed gate electrode 104and damage the gate dielectric layer 110. Such damage may degradeperformance of the semiconductor device 102 and/or lead to failure ofthe semiconductor device 102.

While FIGS. 11-24 are described with reference to various embodiments ofa method, it will be appreciated that the structures shown in FIGS.11-24 are not limited to the method but rather may stand alone separateof the method. While FIGS. 11-24 are described as a series of acts, itwill be appreciated that the order of the acts may be altered in otherembodiments. While FIGS. 11-24 illustrate and describe as a specific setof acts, some acts that are illustrated and/or described may be omittedin other embodiments. Further, acts that are not illustrated and/ordescribed may be included in other embodiments.

With reference to FIGS. 25-29 , a series of cross-sectional views2500-2900 of some alternative embodiments of the method of FIGS. 11-24is provided in which a gate electrode layer has a recessed surfacerecessed relative to a top surface of a gate oxide layer. Thecross-sectional views 2500-2900 correspond to the cross-sectional view500B of FIG. 5B and therefore illustrate formation of the IC and thesemiconductor device 102 in FIG. 5B. However, the method illustrated bythe cross-sectional views 2500-2900 may also be employed to form the ICand/or the semiconductor device 102 in any of FIGS. 1, 3, 4, and 5A-5F.

As illustrated by the cross-sectional view 2500 of FIG. 25 , the recess1104 is formed in the substrate 106. Further, the gate dielectric layer110 and the multilayer film 1202 are deposited lining the recess 1104.The recess 1104, the gate dielectric layer 110, and the multilayer film1202 are formed as illustrated and described respectively with regard toFIGS. 11 and 12 , except that the recessed surface 1204 r of the gateelectrode layer 1204 is recessed below the top surface of the gatedielectric layer 110 by the distance D₂.

As illustrated by the cross-sectional view 2600 of FIG. 26 , the firstplanarization is performed into the second sacrificial layer 1208 asdescribed with regard to FIG. 13 .

As illustrated by the cross-sectional view 2700 of FIG. 27 , the firstand second etches are performed respectively as described with regard toFIGS. 14 and 15 to form the recessed gate electrode 104. Because therecessed surface 1204 r of the gate electrode layer 1204 is recessedbelow the top surface of the gate dielectric layer 110, the first andsecond features 108 a, 108 b are protrusions that protrude upward andthat have top surfaces that are flat or substantially flat. Inalternative embodiments, the top surfaces are curved and/or have someother suitable profile.

As illustrated by the cross-sectional view 2800 of FIG. 28 , the third,fourth, and fifth etches are performed to respectively remove: 1) thefirst sacrificial layer 1206 (see, e.g., FIG. 27 ); 2) the gatedielectric layer 110 at sides of the recessed gate electrode 104; and 3)the second base dielectric layer 1102 (see, e.g., FIG. 27 ). The third,fourth, and fifth etches may, for example, be performed as describedrespectively with regard to FIGS. 16-18 . As discussed above, in atleast some embodiments in which the gate dielectric layer 110 and thefirst sacrificial layer 1206 are or comprise the same material, thethird and fourth etches are performed together by the same act ofetching. Accordingly, in some embodiments, the gate dielectric layer 110and the first sacrificial layer 1206 are removed simultaneously.

As illustrated by the cross-sectional view 2900 of FIG. 29 , the firstand second ILD layers 306 a, 306 b, the CESL 316, the silicide layer310, the source/drain regions 112, the contact vias 308, and the hardmask 312 are formed as described with regard to FIGS. 19-24 .

While FIGS. 25-29 are described with reference to various embodiments ofa method, it will be appreciated that the structures shown in FIGS.25-29 are not limited to the method but rather may stand alone separateof the method. While FIGS. 25-29 are described as a series of acts, itwill be appreciated that the order of the acts may be altered in otherembodiments. While FIGS. 25-29 illustrate and describe as a specific setof acts, some acts that are illustrated and/or described may be omittedin other embodiments. Further, acts that are not illustrated and/ordescribed may be included in other embodiments.

With reference to FIGS. 30-34 , a series of cross-sectional views3000-3400 of some alternative embodiments of the method of FIGS. 11-24is provided in which a gate electrode layer has a recessed surfaceelevated above a top surface of a gate dielectric layer by a greateramount. The cross-sectional views 3000-3400 correspond to thecross-sectional view 500A of FIG. 5A and therefore illustrate formationof the IC and the semiconductor device 102 in FIG. 5A. However, themethod illustrated by the cross-sectional views 3000-3400 may also beemployed to form the IC and/or the semiconductor device 102 in any ofFIGS. 1, 3, 4, and 5A-5F.

As illustrated by the cross-sectional view 3000 of FIG. 30 , the recess1104 is formed in the substrate 106. Further, the gate dielectric layer110 and the multilayer film 1202 are deposited lining the recess 1104.The recess 1104, the gate dielectric layer 110, and the multilayer film1202 are formed as illustrated and described respectively with regard toFIGS. 11 and 12 , except that the thickness T_(g) of the gate electrodelayer 1204 is greater than in FIG. 12 .

As illustrated by the cross-sectional view 3100 of FIG. 31 , the firstplanarization is performed into the second sacrificial layer 1208 asdescribed with regard to FIG. 13 .

As illustrated by the cross-sectional view 3200 of FIG. 32 , the firstand second etches are performed respectively as described with regard toFIGS. 14 and 15 to form the recessed gate electrode 104. Because thethickness T_(g) of the gate electrode layer 1204 is greater than in FIG.15 , the first and second features 108 a, 108 b are more asymmetric thanin FIG. 15 .

As illustrated by the cross-sectional view 3300 of FIG. 33 , the third,fourth, and fifth etches are performed to respectively remove: 1) thefirst sacrificial layer 1206 (see, e.g., FIG. 32 ); 2) the gatedielectric layer 110 at sides of the recessed gate electrode 104; and 3)the second base dielectric layer 1102 (see, e.g., FIG. 32 ). The third,fourth, and fifth etches may, for example, be performed as describedrespectively with regard to FIGS. 16-18 . As discussed above, in atleast some embodiments in which the gate dielectric layer 110 and thefirst sacrificial layer 1206 are or comprise the same material, thethird and fourth etches are performed together by the same act ofetching. Accordingly, in some embodiments, the gate dielectric layer 110and the first sacrificial layer 1206 are removed simultaneously.

As illustrated by the cross-sectional view 3400 of FIG. 34 , the firstand second ILD layers 306 a, 306 b, the CESL 316, the silicide layer310, the source/drain regions 112, the contact vias 308, and the hardmask 312 are formed as described with regard to FIGS. 19-24 .

While FIGS. 30-34 are described with reference to various embodiments ofa method, it will be appreciated that the structures shown in FIGS.30-34 are not limited to the method but rather may stand alone separateof the method. While FIGS. 30-34 are described as a series of acts, itwill be appreciated that the order of the acts may be altered in otherembodiments. While FIGS. 30-34 illustrate and describe as a specific setof acts, some acts that are illustrated and/or described may be omittedin other embodiments. Further, acts that are not illustrated and/ordescribed may be included in other embodiments.

With reference to FIG. 35 , a block diagram 3500 of some embodiments ofthe method of FIGS. 11-34 is provided.

At 3502, a recess is formed in a substrate and a base dielectric layer.See, for example, FIG. 11, 25 , or 30.

At 3504, a gate dielectric layer is deposited lining and partiallyfilling the recess. See, for example, FIG. 12, 25 , or 30.

At 3506, a multilayer film is deposited filling a remainder of therecess over the gate dielectric layer and comprising a gate electrodelayer, a first sacrificial layer over the gate dielectric layer, and asecond sacrificial layer over the first sacrificial layer. See, forexample, FIG. 12, 25 , or 30.

At 3508, a planarization is performed into the second sacrificial layer,wherein the planarization stops on the first sacrificial layer andremoves the second sacrificial layer at sides of the recess. See, forexample, FIG. 13, 26 , or 31.

At 3510, a first etch is performed into the first and the secondsacrificial layers to remove the first sacrificial layer at sides of therecess and to remove or thin the second sacrificial layer over therecess, wherein the second sacrificial layer serves as a mask to protectan underlying portion of the first sacrificial layer. See, for example,FIG. 14, 27 , or 32.

At 3512, a second etch is performed into the gate electrode layer toform a gate electrode in the recess, wherein the second etch stops onthe first sacrificial layer and the gate dielectric layer, and whereinthe first sacrificial layer serves as a mask to protect an underlyingportion of the gate electrode layer. See, for example, FIG. 15, 27 , or32. In some embodiments, the first etch and/or the second etch is/areperformed by dry etching. In some embodiments, the first and secondetches are performed by a common dry etching process in a common processchamber.

At 3514, a series of additional etches is performed to remove the firstsacrificial layer over the gate electrode, the gate dielectric layer atsides of the of the gate electrode, and the base dielectric layer. See,for example, FIGS. 16-18 , FIG. 28 , or FIG. 33 . In some embodiments,the series of etches is performed by wet etching.

At 3516, a hard mask is formed over the gate electrode. See, forexample, FIGS. 19 and 20 , FIG. 29 , or FIG. 34 .

At 3518, source/drain regions are formed in the substrate andrespectively on opposite sides of the gate electrode. See, for example,FIG. 21, 29 , or 34.

At 3520, a silicide layer is formed on the gate electrode and in anopening of the hard mask. See, for example, FIGS. 21-23 , FIG. 29 , orFIG. 34 .

At 3522, contact vias are formed respectively on the silicide layer andthe source/drain regions. See, for example, FIG. 24, 29 , or 34.

While the block diagram 3500 of FIG. 35 is illustrated and describedherein as a series of acts or events, it will be appreciated that theillustrated ordering of such acts or events is not to be interpreted ina limiting sense. For example, some acts may occur in different ordersand/or concurrently with other acts or events apart from thoseillustrated and/or described herein. Further, not all illustrated actsmay be required to implement one or more aspects or embodiments of thedescription herein, and one or more of the acts depicted herein may becarried out in one or more separate acts and/or phases.

With reference to FIGS. 36-43 , a series of cross-sectional views3600-4300 of some alternative embodiments of the method of FIGS. 11-24is provided in which the recessed gate electrode is formed in place of adummy structure. The cross-sectional views 3600-4300 correspond to thecross-sectional view 600 of FIG. 6 and therefore illustrate formation ofthe IC and the semiconductor device 102 in FIG. 6 . However, the methodillustrated by the cross-sectional views 3600-4300 may also be employedto form the IC and/or the semiconductor device 102 in any of FIGS. 7A,7B, 8A-8C, 9, and 10 .

As illustrated by the cross-sectional view 3600 of FIG. 36 , a substrate106 is provided. The substrate 106 underlies and supports a pair ofsource/drain regions 112, a dummy structure 3602, a CESL 316, and afirst ILD layer 306 a. The dummy structure 3602 is laterally between thesource/drain regions 112 and is laterally surrounded by the CESL 316 andthe first ILD layer 306 a. The first ILD layer 306 a overlies thesource/drain regions 112 and is separated from the source/drain regions112 by the CESL 316.

As illustrated by the cross-sectional view 3700 of FIG. 37 , the dummystructure 3602 (see, e.g., FIG. 36 ) is removed to expose or otherwiseform a recess 1104 having a depth D₁. The depth D₁ may, for example, beabout 500-1500 angstroms, about 500-1000 angstroms, about 1000-1500angstroms, about 1000 angstroms, or some other suitable value. Theremoval may, for example, be performed by a photolithography/etchingprocess or some other suitable process. The photolithography/etchingprocess may, for example, employ a photoresist mask 3702 and/or someother suitable mask overlying the first ILD layer 306 a.

As illustrated by the cross-sectional view 3800 of FIG. 38 , the gatedielectric layer 110 and the multilayer film 1202 are deposited liningthe recess 1104. The gate dielectric layer 110 and the multilayer film1202 are formed as illustrated and described with regard to FIG. 12 .

As illustrated by the cross-sectional view 3900 of FIG. 39 , the firstplanarization is performed into the second sacrificial layer 1208 asdescribed with regard to FIG. 13 .

As illustrated by the cross-sectional view 4000 of FIG. 40 , the firstand second etches are performed into the multilayer film 1202 (see,e.g., FIG. 39 ) to form the recessed gate electrode 104 as describedwith regard to FIGS. 14 and 15 .

As illustrated by the cross-sectional view 4100 of FIG. 41 , the thirdand fourth etches are performed to remove: 1) the first sacrificiallayer 1206 (see, e.g., FIG. 40 ); and 2) the gate dielectric layer 110at sides of the recessed gate electrode 104. The third and fourth etchesmay, for example, be performed as described with regard to FIGS. 16 and17 .

As illustrated by the cross-sectional view 4200 of FIG. 42 , thesilicide layer 310 is formed on the recessed gate electrode 104. Thesilicide layer 310 may, for example, be formed by a salicide processand/or some other suitable silicide formation process.

As illustrated by the cross-sectional view 4300 of FIG. 43 , the secondILD layer 306 b and the contact vias 308 are formed as described withregard to FIG. 24 .

While FIGS. 36-43 are described with reference to various embodiments ofa method, it will be appreciated that the structures shown in FIGS.36-43 are not limited to the method but rather may stand alone separateof the method. While FIGS. 36-43 are described as a series of acts, itwill be appreciated that the order of the acts may be altered in otherembodiments. While FIGS. 36-43 illustrate and describe as a specific setof acts, some acts that are illustrated and/or described may be omittedin other embodiments. Further, acts that are not illustrated and/ordescribed may be included in other embodiments.

With reference to FIGS. 44-49 , a series of cross-sectional views4400-4900 of some alternative embodiments of the method of FIGS. 36-43is provided in which a gate electrode layer has a recessed surfacerecessed relative to a top surface of a gate oxide layer. Thecross-sectional views 4400-4900 correspond to the cross-sectional view800B of FIG. 8B and therefore illustrate formation of the IC and thesemiconductor device 102 in FIG. 8B. However, the method illustrated bythe cross-sectional views 4400-4900 may also be employed to form the ICand/or the semiconductor device 102 in any of FIGS. 6, 7A, 7B, 8A, 8C,9, and 10 .

As illustrated by the cross-sectional view 4400 of FIG. 44 , the recess1104 is formed. Further, the gate dielectric layer 110 and themultilayer film 1202 are deposited lining the recess 1104. The recess1104 is formed as described with regard to FIGS. 36 and 37 . The gatedielectric layer 110 and the multilayer film 1202 are formed asillustrated and described respectively with regard to FIGS. 11 and 12 ,except that the recessed surface 1204 r of the gate electrode layer 1204is recessed below the top surface of the gate dielectric layer 110 bythe distance D₂.

As illustrated by the cross-sectional view 4500 of FIG. 45 , the firstplanarization is performed into the second sacrificial layer 1208 asdescribed with regard to FIG. 13 .

As illustrated by the cross-sectional view 4600 of FIG. 46 , the firstand second etches are performed respectively as described with regard toFIGS. 14 and 15 to form the recessed gate electrode 104. Because therecessed surface 1204 r of the gate electrode layer 1204 is recessedbelow the top surface of the gate dielectric layer 110, the first andsecond features 108 a, 108 b are protrusions instead of recesses.

As illustrated by the cross-sectional view 4700 of FIG. 47 , the thirdand fourth etches are performed to respectively remove: 1) the firstsacrificial layer 1206 (see, e.g., FIG. 46 ); and 2) the gate dielectriclayer 110 at sides of the recessed gate electrode 104. The third andfourth etches may, for example, be performed as described with regard toFIGS. 16 and 17 .

As illustrated by the cross-sectional view 4800 of FIG. 48 , thesilicide layer 310 is formed on the recessed gate electrode 104. Thesilicide layer 310 may, for example, be formed by a salicide processand/or some other suitable silicide formation process.

As illustrated by the cross-sectional view 4900 of FIG. 49 , the secondILD layer 306 b and the contact vias 308 are formed as described withregard to FIG. 24 .

While FIGS. 44-49 are described with reference to various embodiments ofa method, it will be appreciated that the structures shown in FIGS.44-49 are not limited to the method but rather may stand alone separateof the method. While FIGS. 44-49 are described as a series of acts, itwill be appreciated that the order of the acts may be altered in otherembodiments. While FIGS. 44-49 illustrate and describe as a specific setof acts, some acts that are illustrated and/or described may be omittedin other embodiments. Further, acts that are not illustrated and/ordescribed may be included in other embodiments.

With reference to FIG. 50 , a block diagram of some embodiments of themethod of FIGS. 36-49 is provided.

At 5002, a dummy structure that overlies a substrate is removed to forma recess, wherein the recess is between source/drain regions. See, forexample, FIGS. 36 and 37 or FIG. 44 .

At 5004, a gate dielectric layer is deposited lining and partiallyfilling the recess. See, for example, FIG. 38 or 44 .

At 5006, a multilayer film is deposited filling a remainder of therecess over the gate dielectric layer and comprising a gate electrodelayer, a first sacrificial layer over the gate dielectric layer, and asecond sacrificial layer over the first sacrificial layer. See, forexample, FIG. 38 or 44 .

At 5008, a planarization is performed into the multilayer film, whereinthe planarization stops on the first sacrificial layer and removes thesecond sacrificial layer at sides of the recess. See, for example, FIG.39 or 45 .

At 5010, a first etch is performed into the first and the secondsacrificial layers to remove the first sacrificial layer at sides of therecess and to remove or thin the second sacrificial layer over therecess, wherein the second sacrificial layer serves as a mask to protectan underlying portion of the first sacrificial layer. See, for example,FIG. 40 or 46 .

At 5012, a second etch is performed into the gate electrode layer toform a gate electrode in the recess, wherein the second etch stops onthe first sacrificial layer and the gate dielectric layer, and whereinthe first sacrificial layer serves as a mask to protect an underlyingportion of the gate electrode layer. See, for example, FIG. 40 or 46 .In some embodiments, the first etch and/or the second etch is/areperformed by dry etching. In some embodiments, the first and secondetches are performed by a common dry etching process in a common processchamber.

At 5014, a series of additional etches is performed to remove the firstsacrificial layer over the gate electrode and the gate dielectric layerat sides of the of the gate electrode. See, for example, FIG. 41 or 47 .In some embodiments, the series of etches is performed by wet etching.

At 5016, a silicide layer is formed on gate electrode. See, for example,FIG. 42 or 48 .

At 5018, contact vias are formed respectively on the silicide layer andthe source/drain regions. See, for example, FIG. 43 or 49 .

While the block diagram 5000 of FIG. 50 is illustrated and describedherein as a series of acts or events, it will be appreciated that theillustrated ordering of such acts or events is not to be interpreted ina limiting sense. For example, some acts may occur in different ordersand/or concurrently with other acts or events apart from thoseillustrated and/or described herein. Further, not all illustrated actsmay be required to implement one or more aspects or embodiments of thedescription herein, and one or more of the acts depicted herein may becarried out in one or more separate acts and/or phases.

In some embodiments, the present disclosure provides a semiconductordevice including: a substrate; a pair of source/drain regions in thesubstrate; a gate dielectric layer overlying the substrate; and a gateelectrode recessed into a top of the gate dielectric layer and laterallybetween the source/drain regions, wherein a top surface of the gateelectrode has a first edge and a second edge respectively on oppositesides of the gate electrode, wherein a thickness of the gate electrodeis substantially uniform from the first edge to the second edge, andwherein the gate electrode has a pair of features respectively at thefirst and second edges. In some embodiments, the features are invertedrounded corners. In some embodiments, the features are upwardprotrusions. In some embodiments, the features are concave recesses. Insome embodiments, the pair of features includes a first feature and asecond feature respectively having a first cross-sectional profile and asecond cross-sectional profile, wherein the first cross-sectionalprofile is a mirror image of the second cross-sectional profile. In someembodiments, the features are different regions of a common feature thatextends laterally in a closed path to surround the top surface of thegate electrode. In some embodiments, the gate electrode is recessed intoa top of the substrate and is separated from the substrate by the gatedielectric layer. In some embodiments, the substrate defines a finprotruding upward, wherein the gate electrode wraps around a top of thefin.

In some embodiments, the present disclosure provides an IC including: asubstrate; a pair of source/drain regions in the substrate; a gateelectrode laterally between the source/drain regions, wherein a top ofthe gate electrode has a feature extending laterally in a closed pathalong a periphery of the gate electrode, wherein the feature has a firstsegment and a second segment respectively on opposite sides of the gateelectrode, wherein the top of the gate electrode is substantially flatfrom the first segment to the second segment, and wherein the feature isa protrusion or a depression; and a gate dielectric layer wrappingaround a bottom of the gate electrode from a sidewall of the gateelectrode to a bottom surface of the gate electrode. In someembodiments, the feature is a protrusion protruding upward. In someembodiments, the feature is an inverted corner that arcs downward with adecreasing slope from a top surface of the gate electrode to a sidewallof the gate electrode. In some embodiments, the feature is a recess. Insome embodiments, the IC further includes: an ILD layer overlying thesubstrate and the source/drain regions, wherein the gate electrode issunken into a top of the ILD layer, wherein the gate dielectric layerseparates the gate electrode from the substrate and sidewalls of the ILDlayer. In some embodiments, the gate electrode is sunken into a top ofthe substrate, such that a bottom surface of the gate electrode is belowa top surface of the substrate.

In some embodiments, the present disclosure provides a method forforming a semiconductor device, the method including: forming a recessoverlying a substrate; depositing a gate dielectric layer lining andpartially filling the recess; depositing a multilayer film filling aremainder of the recess over the gate dielectric layer and including agate electrode layer, a first sacrificial layer over the gate electrodelayer, and a second sacrificial layer over the first sacrificial layer;performing a planarization into the second sacrificial layer that stopson the first sacrificial layer and removes the second sacrificial layerat sides of the recess; performing a first etch into the first andsecond sacrificial layers to remove the first sacrificial layer at thesides of the recess; and performing a second etch into the gateelectrode layer using the first sacrificial layer as a mask to removethe gate electrode layer at the sides of the recess and to form a gateelectrode underlying the first sacrificial layer in the recess. In someembodiments, the first and second etches are performed by a common dryetching process. In some embodiments, the first etch is a non-selectiveetch having substantially the same etch rates for the first and secondsacrificial layers, and wherein the second etch is a selective etchhaving a high etch rate for the gate electrode layer relative to thefirst sacrificial layer. In some embodiments, the method furtherincludes: performing a third etch into the first sacrificial layer afterthe second etch to remove the first sacrificial layer from atop the gateelectrode; and performing a fourth etch to remove the gate dielectriclayer at sides of the recess. In some embodiments, the third and fourthetches are performed by a common wet etching process using the sameetchant. In some embodiments, the forming of the recess includesperforming an etch into the substrate to form the recess in thesubstrate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device comprising: a substrate; apair of source/drain regions in the substrate; a gate dielectric layeroverlying the substrate; a gate electrode recessed into a top of thegate dielectric layer and laterally between the source/drain regions,wherein a top surface of the gate electrode has a first edge and asecond edge respectively on opposite sides of the gate electrode,wherein a thickness of the gate electrode is substantially uniform fromthe first edge to the second edge, and wherein the gate electrode has apair of features respectively at the first and second edges; and asilicide layer atop the gate electrode, wherein the silicide layer isbetween the first edge and the second edge and is spaced from the pairof features.
 2. The semiconductor device according to claim 1, whereinthe features are inverted rounded corners.
 3. The semiconductor deviceaccording to claim 1, wherein the features are upward protrusions. 4.The semiconductor device according to claim 1, wherein the features areconcave recesses.
 5. The semiconductor device according to claim 1,wherein the pair of features comprises a first feature and a secondfeature respectively having a first cross-sectional profile and a secondcross-sectional profile, and wherein the first cross-sectional profileis a mirror image of the second cross-sectional profile.
 6. Thesemiconductor device according to claim 1, wherein the gate electrode isrecessed into a top of the substrate and is separated from the substrateby the gate dielectric layer.
 7. The semiconductor device according toclaim 1, wherein the substrate defines a fin protruding upward, andwherein the gate electrode wraps around a top of the fin.
 8. Thesemiconductor device according to claim 1, wherein the gate electrodeconsists essentially of a single material, and wherein the pair offeatures are recesses or protrusions.
 9. The semiconductor deviceaccording to claim 1, wherein the gate electrode has a flat top surfaceportion from the first edge to the second edge, and further has a pairof curved top surface portions respectively at the pair of features. 10.An integrated circuit comprising: a substrate; a pair of source/drainregions in the substrate; a gate electrode laterally between thesource/drain regions, wherein a top of the gate electrode has a featureextending laterally in a closed path along a periphery of the gateelectrode, wherein the feature has a first segment and a second segmentrespectively on opposite sides of the gate electrode, wherein the top ofthe gate electrode is substantially flat from the first segment to thesecond segment, and wherein the feature is a protrusion or a depression;a gate dielectric layer wrapping around a bottom of the gate electrodefrom a sidewall of the gate electrode to a bottom surface of the gateelectrode; and a hard mask covering the first and second segments of thefeature and on a sidewall of the gate dielectric layer, wherein the hardmask has a pair of sidewall segments facing each other respectively onthe opposite sides of the gate electrode.
 11. The integrated circuitaccording to claim 10, wherein the feature is a protrusion protrudingupward.
 12. The integrated circuit according to claim 10, wherein thefeature is a depression that arcs downward with a decreasing slope froma top surface of the gate electrode to the sidewall of the gateelectrode.
 13. The integrated circuit according to claim 10, wherein thefeature is a depression with a concave profile.
 14. The integratedcircuit according to claim 10, further comprising: an interlayerdielectric (ILD) layer overlying the substrate and the source/drainregions, wherein the gate electrode is sunken into a top of the ILDlayer, and wherein the gate dielectric layer separates the gateelectrode from the substrate and sidewalls of the ILD layer.
 15. Theintegrated circuit according to claim 10, wherein the gate electrode issunken into a top of the substrate, such that the bottom surface of thegate electrode is below a top surface of the substrate.
 16. Theintegrated circuit according to claim 10, wherein the integrated circuitfurther comprises: a contact via extending through the hard mask to thetop of the gate electrode between the sidewall segments of the hardmask.
 17. A semiconductor device comprising: a substrate; a pair ofsource/drain regions in the substrate; a gate electrode overlying thesubstrate between the source/drain regions, wherein the gate electrodehas a flat top surface portion, a first curved top surface portion, anda second curved top surface portion, wherein the first and second curvedtop surface portions border the flat top surface portion respectively onopposite sides of the flat top surface portion and have individualprofiles mirroring each other; a gate dielectric layer separating thegate electrode from the substrate and on a sidewall of the gateelectrode, which borders the first curved top surface portion; and asilicide layer atop the flat top surface portion and spaced from thefirst and second curved top surface portions; wherein the first curvedtop surface portion is elevated relative to the flat top surfaceportion.
 18. The semiconductor device according to claim 17, wherein thefirst and second curved top surface portions correspond to regions of acommon curved top surface portion extending in a closed path around theflat top surface portion at a periphery of the gate electrode.
 19. Thesemiconductor device according to claim 17, further comprising: a hardmask covering the first and second curved top surface portions and on asidewall of the gate dielectric layer, wherein the hard mask has a pairof sidewall segments facing each other respectively on the oppositesides of the flat top surface portion; and a contact via extendingthrough the hard mask to the flat top surface portion between thesidewall segments.
 20. The semiconductor device according to claim 17,wherein the silicide layer comprises nickel silicide.